Hot Brakes Vs Max Reversers on landing.

[Anp]

To save more fuel, it is being advised these days that landings should be in Config 3 and idle reverse should be used for the landing runs. The consequent rise in brake temperatures and brake wear works out to be less costly for the company. My question is, will subjecting wheels to temps of 300+ regularly have any detrimental effect on their life? Yes all 320's in our company have brake fans.
Thanks!

[lomapaseo]

The answer to your simple question is probably yes. However as your company has said, brake costs are far less expensive than reverser caused wear (maintenance, cost of ownership, FOD etc.).

There are obviously trades, but it sounds to me like your company has considered and chosen something reasonable.

[dixi188]

Carbon brakes like to be at around 300 C. Least wear and most efficient. Also the wear is related to the number of applications and not the energy absorbed. (At least that is what we were told when we had carbon brakes fitted to the A300).

As an aside, back in the early '80s, on the BAC 1-11, Laker were using reverse idle and lots of brakes whereas BCAL were using lots of reverse and little brakes. I don't know which was more cost effective, but Laker went bust and BCAL was swollowed up by BA.

[Bruce Waddington]

Dixi188

The statement you make about brake temperature is only party true. The Yahoo Airbus Discussion Group has some wonderful information on Carbon Brake wear and it is indeed directly tied to the number of applications and the temperature of the brake. At lower temperatures the wear per application is higher. As the temperature of the brake increases there will be a decrease in wear per application and then an increase in wear per application as the temperature rises even higher.

The graph for each brake manufacturer approved for the Airbus fleet varies somewhat (wear rates and temperatures), but the general pattern is similar for each one.

But, and this is a huge but, the brakes do not work better if they are hot. A brake can only absorb a limited amount of energy before it fails and the hotter a brake is to start with the less energy it can absorb during a rejected take-off before that failure takes place. Some of the mob I worked for taught this concept of 'hotter brakes work better' and it was always my opinion ... well we won't get into that ... enough to say that the concept is incorrect.

best regards,

Bruce Waddington

[stilton]

Point well made, the 'hot brakes work better' myth is a very widespread one.

No question that the Carbon units can absorb more energy and are lighter but
they have their limits.

[Lookleft]

A major international airline put this theory into practise and made it SOP on the B744. One of their aircraft overan a wet runway because they hadn't cleared the procedure with the manufacturer. Until certification is based on a reduced flap reverse idle technique stick with what is tried and tested.

[Rainboe]

Wasn't that the one where they weren't even selecting reverse idle, and landed wet and deep and still didn't select any reverse until too late? BA always uses reverse idle and medium or light autobrakes unless more is needed. It is not just economy- reverse power is darn noisy, and that is a major factor in our responsibilities these days. I've had to override a copilot who, as a matter of course, was so unthinking that he used a lot of reverse power at LGW at 3.30 in the morning! Embarrasing. Where do they get them?

[wisperingwillows]

Hi!,

The ideal temperature for brake usage depends on the type of brakes your company has but as a general rule brakes work best above 80 to 100 C..

The reason for the brakes hot warning at 300C in the A320 is to prevent the brakes from getting hot enough in the wheel bay to ignite any leaking hydraulic fluid and cause a fire in the wheel bay.

Also, there is an issue with the brakes over 300C giving rated performance in case of a rejected T/O.

Remember fuel saving is ok but if you go out of the runway only you & your license will be held responsible.....

[HercDriver]

My personal technique is to use what the situation requires. If I have plenty of runway.... I will idle reverse and use brakes as necessary to slow and turn off. On shorter runways I will use appropriate reverser thrust to slow the aircraft. Common sense wins in my thought at least.

[autoflight]

If your company has chosen a policy, it really doesn't matter too much. Operating into the shorter runway at BRU with one aircraft 3.75 NM ahead and another 3.75 NM behind was another matter. Delay braking to take high speed taxiway at a reasonable clip. If any aircraft did otherwise under these conditions go-around were guaranteed.
It was obvious that our little airline got preferential treatment fro ATC as a result. Those preferences were worth a lot more than a bit of brake or engine wear.

[Dragon 1]

For A320, my understanding is that the Auto Brakes provide a deceleration rate. Whether you use reverse thrust or not, the rate of deceleration will be the same. Personally, I dont see the point in using revers thrust under normal circumstances. As has been said, you wont wear out the brakes any sooner by not using reverse thrust. Alot of noise, fuel, vibration through the airframe and mechanical wear and tear on the engines for little or no effective gain.

[PENKO]

Dragon, that only counts for autobrake medium and low. The day that you really need to brake to save your behind you will be pressing the brakes all the way down to the stops. In this situation of course, reverse thrust will add to the total braking, and might just give you that extra bit of deceleration you need. The trick is to know in advance if you 'might' need this extra braking.

[Bruce Waddington]

Dragon 1,

You write, "...... Alot of noise, fuel, vibration through the airframe and mechanical wear and tear on the engines for little or no effective gain."

Reverse thrust, applied at high speed, can be an effective way to dissipate energy during the landing roll. Even more so when the runway has a low coefficient of braking.

Remember, there are only four ways to slow the aircraft after landing;

1. Aerodynamic drag .... not very effective
2. Brakes ... can be very effective
3. Reverse thrust ... can be effective if used at high speeds
4. Running into a solid object ... very effective, but hard on all concerned

My students were all given the same advice. Look ahead at the runway you will be landing on. How long is it ? Is it dry or contaminated ? Where are the preferred exits ? Are High Intensity Runway Operations in effect ? Do I have a short turn around time ? What is the outside air temperature ?

When you have all that information pick an energy dissipation configuration that suits the landing. Use flap, brake and reverse selections to optimize the landing. For example, on a long dry runway where you will be turning off near the far end and have no turn around time constraints I would use Flap 3, Auto Brake Off and Idle Reverse. On a short contaminated runway my choice would be Flap Full, Auto Brake Medium and Max Reverse.

The point is to be a thinking pilot and use the tools you have at your disposal in a safe and efficient manner.

best regards,

Bruce Waddington

[blade]

So if a brake cooling schedule for carbon brakes says to wait say 55mins before another T/O is this to prevent wheelwell fires or to improve RTO energy absorption or to ensure you dont get a fire after a subsequent RTO.

[Dragon 1]

Thanks for the flying lesson guys.
Vapp of 141kts at 180 tonnes (A330) gives you a landing distance of 1045m Then you subtract 1%( FCOM 2), yes that is right, 1% if you have resvers thrust operative, then multiply by the factored distance, which where I am from is 1.67%. 1% is 10.5m. That is less than the cockpit cutoff angle. By the time you get the reverser`s out and working at their maximum capacity you are down near 120kts. Airbus recommend you stow them at 70kts. So you would get 50kts max of use out of them. As I said NORMAL CIRCUMSTANCES. Touch down in the touch down zone on a dry uncontaminated runway, would constiute normal circumstances with NO SOLID OBJECTS at the end of it.
So back to my original comment, which has been quoted twice, 1% is little or no effective gain.
The topic of the thread was brake temp V`s MAX REVERS. Not revers idle, or using manual braking if required.
Of course if the the runway is short, wet or contaminated or you are going run off the end of the runway you would use everything available to you to stop.

[Old Fella]

The use of Reverse Thrust to wash off speed is very effective and is how the aircraft manufacturers intended the aircraft to be operated. Full Reverse held in until below 100 Kts and cancelled by 60 Kts might disturb a few natives but will surely save on brakes. The same applies to the use of Flap for landing. The manufacturer provides a Full Flap position with the expectation that it will be used. The bean counters and the environmentalists have hijacked the operations departments to the detriment of the overall operation in some companies. How much money did the Flap 25/Idle Reverse configuration save Qantas, or at least their insurers? Not much I suggest when you deduct the $100 Million plus it cost to repair the Bangkok over-run aircraft.

[Centaurus]

you wont wear out the brakes any sooner by not using reverse thrust.

About 30 years ago an article was published by the brake manufacturer of the brakes on the DC9 titled "The High Cost of Hard Braking" It tabulated in dollar terms the relative costs of braking at various speeds versus reverse thrust from idle reverse to full reverse.

I'll try and locate the article but the conclusion was crystal clear. With idle reverse the cost of brake wear and tear were almost doubled. Of course these were not carbon brakes. But I find it difficult to understand that pilots who advocate idle reverse and significant braking are seemingly oblivious of the potential dangers associated with hot brakes. I recall an old Boeing bulletin stating if you could not place your hand on the brake units then by definition the brakes were hot and appropriate delays required.

[guiones]

Bruce:

I agree with your posts, but I have a problem with "On a short contaminated runway my choice would be Flap Full, Auto Brake Medium and Max Reverse".

I don't know how short a rwy you are operating, but for certain rwys MED A/B is not enough or the safest alternative. Yes, I know it helps with lateral control, but in certain areas the A320 series is operated; manual braking is the norm to get better action than MED.

I know you said "my choice" but consider that max performance braking, the way Test Pilots certify the Airbuses is max pedal pressure on touch down.


G

[Bruce Waddington]

quiones,

My first choice , if between MED and MAX brake is required would be to look for another airport to land at. But each crew has their own opinion about that sort of thing.

Dragon 1

Sorry you felt I was "'giving you a flying lesson". That was never the intent. And, as you have reminded us the topic is hot brakes vs max reverse and the effects thereof.

The numbers you have put out do not reflect the reality of line operations. They are determined with the following conditions;

1. Speed at the threshold is VLS
2. Altitude at the threshold is 50 feet agl
3. Thrust levers to idle at 50 feet agl
4. Very little flare
5. Auto Spoiler deployment
6. Max brake applied and held until a complete stop

The time available for reverse to work in this situation is minimal and therefore the the one percent reduction in actual stoppping distance.

But in line operations we do not apply and hold max brake for landing. The reason of course is that the fuse plugs would melt, the brakes would probably seize and the chance of a brake fire is greatly increased.

Therefore the distance saved by using max reverse in line operations is much higher than the distance saved in the certification tests.

There is no doubt that Flap 3 approaches and landings save fuel. Idle reverse saves fuel and noise. But brake temperatures will rise to above 300 very quickly since they are providing the bulk of the deceleration. Does this impact the life of the brake ... of course it does, but the mob that I worked had leased brakes so did not care about shortening their useful life. The cost of fuel and engine maintenance was less than the cost of changing out the brakes.

regards,

Bruce Waddington

edited for grammar, not content

[backofthedrag]

My airline esablished this procedure to save fuel. In 400 landings since , I have seen one where open descent was selected at 39000 ft. Gradual deceleration to 1000 ft - no speed brake to 1000 when the thrust came on Flap 3 at Vapp. ( not me guv ) The other 399 were mainly overushed , unstabilised and often called for a go-around at 500 ft. The best were flap full and stabilised a little before 1000ft with a landing assured.
The brakes are there to brake and reverse trust is available as required depending on the turn-off aimed at- but this is a skill to be learned after a consistent stabilised approach.

[PENKO]

Of course you need to think about where and when you use Flaps 3. If there are strong thermals near the runway, forget about it, you'll have a hard time to reach Vapp. Same if there is a strong tailwind. And anyhow, if you briefed for Flaps 3 and for whatever reason it does not realy work out for you, reconfigure for Flaps Full before 1000' and presto, on you go.

But backofthedrag, if you need just a little bit of speedbrake to set you up for a Flap 3 landing, then what is wrong with that? No shame there. At least you're not 'abusing' the superduperspeadbrakes called Faps Full that mask all but the greatest energy management mistakes.